I would submit based on my experiences that without the threat or intent of atemi, that aikido really does not work very well.

Interesting.

In my understanding, for any locking, pinning, takedown or throwing technique to work, there must be a disruption of balance (physical, mental etc.) of some sort. This can be achieved via atemi, movement, distractions and other means.

Since Aikido is an expression of Jujutsu it would make sense that disruption of balance (a la atemi or otherwise) would be necessary for any of the above mentioned categories of techniques to work. The same thing would apply for any other art that involves locking, pinning, takedown and throwing techniques. A person in balance can pretty much shut down any technique if he really wants to, the particular style or method he is practicing is irrelevant imo.

Think about it, are there any styles that apply locks or throws that actually work on a resistant opponent without first taking his balance (physical or otherwise) or distracting him? I haven't found one so far.

For those who drill and train seriously in it, kuzushi utilising positioning and movement is another aspect of Aikido that makes its techniques very viable against skilled resistance. Like atemi however, kuzushi by movement alone has its limitations so it is good to know and study as many ways as possible to disrupt the balance of your attacker.